Updating my situation...
I've been using my original Gigabyte G1 Gaming 970 card very happily on my Dell IPS 2407 monitor.
I've tried putting the Gigabyte G1 Gaming 1070 back in my machine (the kids had been using it happily of late), and although it's less 'bad' on my eyes than reported originally, presumably due to driver updates, it's still no good. It leaves me feeling queasy and sorta green round the gills. After I put the 970 back in everything goes back to normal.
Today I've gotten an ASUS Strix 1080 card to trial. My initial tests show it causes the same problems as the 1070 - and leaves me feeling pretty rotten after using it. It's not as bad as some laptops I've tried including my wife's newish Acer/Nvidia 950 system, but it's still not looking very promising. This strongly suggests there's something very different going on in the new Pascal architecture output rendering compared with the previous generation of cards - and these are the first video cards I've found that cause me problems.
Add to that list both sizes of iPad Pro models that had to be sent back to Apple as they too left me feeling 'odd', leaving me on the sorta-OK iPad Air 2/iPhone 6S combo. And, then there's the two new high spec IPS and VA panels I tried and couldn't use, and had to return.
So I'm now resigned to having to give this generation of 10-series Nvidia cards a complete miss (as well as new iPads, and most screens - something that is very difficult to test). For someone in IT and who likes his flight-sims, being stuck on on old CFL backlight screens and last-gen video cards is a very bitter pill to swallow.
I cannot precisely pin down my problem(s). I know PWM can contribute to the effects I experience but there's none active on my screen at high brightness levels (offset in the video card settings). On a problematic screen I had for a time, it had low blue light controls that I tried with no real improvement in symptoms. That same screen had no PWM and very high refresh rates but they didn't help. I've gotten my eyes checked and wear glasses but then I'm OK on some screens and not others, glasses or not so that's seemingly not the root cause. Then there's the 10 series Nvidia cards... that make me wonder - just what is it that they're doing to cause these problems?